Process for control of boost pressure limitation of a turbocharger in an internal combustion engine as a function of the density of ambient air

ABSTRACT

The invention relates to a process for control of limitation of the boost pressure of a turbocharger in an internal combustion engine as a function of the density of ambient air, the values determined for the actual ambient temperature T ∞ , for the actual ambient pressure p ∞ , for the air mass m L  drawn in, and for the boost pressure p L  being determined in this operating condition at assigned intervals and the actual pressure p VE  at the compressor intake and the actual temperature T VE  at the compressor intake being determined from these values by way of predetermined air mass dependent correction characteristics, the air mass throughput m Lkor  adjusted to the rated conditions of the compressor being determined at the compressor intake respectively from the temperature T VE  determined at the compressor intake and from the air mass m L , the compressor speed dependent maximum permissible boost pressure p Lmaxkor  being taken respectively from the compressor characteristic for the maximum permissible turbocharger speed n vmax  at this adjusted air mass throughput m Lkor  at the compressor intake adjusted to standard conditions of the compressor and from ambient pressure p ∞  as determined and being compared with the boost pressure p List  determined in this operating condition, and the boost pressure being adjusted so that the value determined for the boost pressure p List  corresponds at the maximum to the respective maximum permissible boost pressure p Lmaxkor  or determined in this condition.

[0001] The invention relates to a process for control of boost pressure of a turbocharger in an internal combustion engine as a function of the density of ambient air, an internal combustion engine with exhaust gas turbocharger and with control means for control of the boost pressure in which the actual boost pressure is determined at specific time intervals and compared with assigned values for the desired boost pressure taken from stored compressor characteristics and readjusted, and with an engine control device for an internal combustion engine with exhaust gas turbocharger having a control unit for control of the boost pressure and a data storage unit.

[0002] Control of the boost pressure of an internal combustion engine with a turbocharger is of the state of the art. For example, DE 197 57 661 C1 discloses boost pressure control in an internal combustion engine with turbocharger in which a desired boost pressure is determined from characteristics determined by engine speed and load and is taken into account for control of unstable influences based on dynamic road behavior.

[0003] As soon as the supercharger speed exceeds a maximum permissible boundary value for the supercharger speed, a turbocharger can be damaged. Such excessive speed may come about if the vehicle is in operation at higher altitudes in which the ambient pressure falls below a specific minimum pressure or the absorption line of the engine changes radically as a result of leaks from the system. In order to prevent overspeed of the turbocharger in operation at a high altitude, the speed of the turbocharger is usually restricted by limiting the boost pressure as a function of the engine speed and atmospheric pressure. This is accomplished by means of previously recorded characteristics in which the boost pressure is filed on the basis of ambient pressure and engine speed. For this purpose costly tests for determining the characteristics must be carried out in advance for each altitude for every engine having a turbocharger. In addition, fluctuations in air pressure and in ambient temperature must be predicted in the design process.

[0004] The object of the invention is to limit overspeed of the turbocharger in an internal combustion engine having a turbocharger by a simple and reliable process in which allowance is made for atmospheric conditions despite high performance.

[0005] It is claimed for the invention that this object is attained both by the process for control of boost pressure limitation of a turbocharger in an internal combustion engine as a function of the density of ambient air in accordance with the characteristics specified in claim 1 and by designing an internal combustion engine having a exhaust gas turbocharger and by means for control of the boost pressure in which the actual boost pressure is determined at specific time intervals and compared with assigned values for the desired boost pressure in a particular operational condition determined from stored compressor characteristics and reset, in accordance with the characteristics specified in claim 9, and by means of an engine control device for an internal combustion engine with exhaust gas turbocharger having a control unit for adjustment of the boost pressure and a data storage unit in accordance with the characteristics specified in claim 10.

[0006] As a result, the boost pressure as a function of atmospheric conditions is determined simply at each determination point, with the atmospheric conditions taken into account, and this boost pressure is compared with the maximum boost pressure permissible for this operating condition. Without costly pretesting for determination of a set of characteristics for each individual ambient situation the measured boost pressure may be compared directly with the maximum permissible boost pressure taken from a set of characteristics to determine if the compressor speed is still below the boundary with overspeed and accordingly to prevent further increase when the boundary state is reached.

[0007] By preference the process as specified in claim 2, in which the adjusted air mass throughput at the compressor intake may be determined with very good approximation, is to be carried out.

[0008] The process as specified in claim 3 permits control and boost pressure limitation in a simple manner by means of the engine control means usually already present as part of the structure, means in which all predetermined data are present and to which all measured data are first delivered through corresponding inputs and from which corresponding control signals for boost pressure control may be forwarded by way of an output.

[0009] The process as specified in claim 4 permits especially precise determination of the pressure relationships P_(L)P_(VE) by taking into account the pressure losses between measuring point and compressor intake. This makes it possible further to minimize the confidence interval between maximum permissible compressor speed and compressor speed as measured. The performance spectrum of the engine may in this way be extended directly to higher levels.

[0010] Preference is to be given to the process as specified in claim 5, a process by which it is possible additionally to minimize the danger of short-term occurrence of boost pressure peaks situated above the maximum permissible boost pressure and accordingly the occurrence of short-term compressor speed peaks situated above the maximum permissible value for the compressor speed on the basis of dynamic processes. Overspeed of the compressor as a result of dynamic processes and the speed peaks caused by them can thus be prevented by simple means.

[0011] Claims 6 to 8 represent especially advantageous processes for control of boost pressure limitation.

[0012] The invention is described in detail in what follows with reference to the exemplary embodiments presented in FIGS. 1 to 3, of which

[0013]FIG. 1 presents a schematic diagram of an internal combustion engine with turbocharger;

[0014]FIG. 2 a control graph illustrating control of boost pressure limitation as claimed for the invention;

[0015]FIG. 3 a qualitative representation of a set of compressor characteristics.

[0016]FIG. 1 shows an internal combustion engine 1 to which exhaust gases are transferred by a conventional methods by way of a suction pipe 2 which delivers charged air by way of a turbocharger 4 and from which exhaust gases are delivered by way of a exhaust gas line 15 to the turbine 6 of the turbocharger 4, if supercharging is desired. When the turbocharger 4 is operated, the turbine 6 of the turbocharger 4 is driven by the exhaust gases, the process being accompanied by stress relief, and the exhaust gases are transferred from the turbine 6 by a conventional method by way of a exhaust gas line 16. The turbine 6 of the turbocharger 4 drives the compressor 5 of the turbocharger by a conventional method, as a result of which the air drawn in by way of an air duct 13 and moving through an air filter 12, an air duct 11, an air mass gauge 10, and an air duct 9, is supercharged and while in this supercharged state is delivered by conventional means by way of an air duct 8, a boost air cooler 3, an air duct 7, to the intake pipe 2 and accordingly the engine 1. Supercharging of the boost air by the turbocharger 4 is controlled by state-of-the-art conventional means (not shown) in accordance with the desired performance requirements.

[0017] In order to limit the supercharger speed to prevent overspeed of the turbocharger under charged atmospheric conditions, such as at higher altitudes, the supercharger pressure p_(List), the ambient temperature T_(∞), and the ambient pressure P_(∞), and, by way of the air mass gauge 10, the air mass m_(L) drawn in and by way of a boost pressure and supercharge air temperature sensor 17 the boost pressure p_(List) are measured in this operational situation. The measurement data are transmitted to the calculation unit 20 of the engine control device 18. The set of compressor characteristics specific to the turbocharger 4 is stored in a databank 19 of conventional design of the engine control device 18.

[0018] As is to be seen from FIG. 3, this specific set of compressor characteristics shows among other things the characteristic curve of the maximum permissible compressor speed n_(vmax) plotted against the air mass m_(Lkor) adjusted to the standard condition of the compressor and the pressure ratio of the boost pressure downstream from the compressor p_(L) to the pressure upstream from the compressor P_(VE).

[0019] As is to be seen from FIG. 2, the temperature at the compressor intake T_(VE) is determined in the calculation unit 20 of the engine control device 18 from the ambient temperature T_(∞), allowance being made for a stored, predetermined, air mass dependent correction curve value K_(T), as also the pressure at the compressor intake is determined from the ambient pressure P_(∞) by application of a stored, predetermined, air mass dependent correction curve value K_(P) at the compressor intake P_(VE).

[0020] The correction curves K_(T) and K_(P) may, for example, be stored in the form of air mass dependent correction factors. The calculation unit 20 then calculates the air mass throughput at the compressor intake m_(Lkor) adjusted to standard conditions, from the value for the air mass drawn in, m_(L), the value for the temperature at the compressor intake, T_(VE), and the value for the pressure at the compressor intake, P_(VE), in accordance with the following formula:

m _(Lkor) =m _(L)·((T _(VE)+273.15 K)/T _(OV))^(0.5)/(p _(VE) /P _(OV))),

[0021] T_(OV) being the standard temperature and P_(OV) the standard pressure of the compressor characteristic. The standard conditions are the conditions under which the compressor characteristic was plotted.

[0022] The maximum permissible boost pressure ratio (p_(L)/P_(VE)) of boost pressure p_(L) to pressure upstream from compressor P_(VE) to be associated with the value determined for the adjusted air mass drawn in at the compressor intake m_(Lkor) at the maximum permissible computer speed n_(Vmax) is determined from the compressor characteristic stored in the databank 19. By multiplication by the pressure determined upstream from the compressor P_(VE) this value is determined for the maximum permissible boost pressure P_(Lmax) for the air mass throughput at this turbocharger 4.

[0023] The computed maximum permissible boost pressure P_(Lmax) is adjusted to an adjusted maximum permissible boost pressure p_(Lmaxkor) in accordance with the equation

p _(Lmaxkor) =p _(Lmax) ·K _(PLLK), with K _(PLLK) =f(m _(L)),

[0024] by means of a predetermined correction factor K_(PLLK) stored in the databank 20 [sic] for the boost pressure loss between boost pressure value measured at the position of the boost pressure sensor 17 and the compressor outlet immediately downstream from the compressor 5, in particular because of the high pressure loss in the boost cooler 3.

[0025] This corrected, maximum permissible, atmosphere dependent boost pressure p_(Lmaxkor) as determined is compared with the measured boost pressure p_(L).

[0026] So long as the boost pressure p_(L) is smaller than the maximum permissible adjusted boost pressure p_(Lmaxkor), according to the compressor performance characteristic in FIG. 3, the compressor speed n_(v) corresponding to this state is smaller than the maximum permissible compressor speed n_(Vmax). Resort to boost pressure adjustment is not yet necessary. As soon as the boost pressure p_(L) corresponds to the maximum permissible boost pressure p_(Lmaxkor), action is taken so that adjustment for the time being no longer allows boost pressure increase in this condition.

[0027] In another embodiment short-term overspeed due to peak boost pressures generated by dynamic processes can be counteracted, after calculation of the maximum permissible pressure ratio (P_(L)/P_(VE))_(max) or after calculation of the adjusted maximum permissible boost pressure p_(Lmaxkor) allowing for pressure losses, by making an adjustment of the maximum permissible pressure ratio allowing for the gradient of the turbocharger speed over time, through application of a predetermined correction parameter K_(n) stored in the databank 20 [sic.], so that a corrected, maximum permissible pressure ratio (P_(L)/P_(VE))_(maxn) taking the speed changes of the supercharger into account is determined, one which corresponds, for example, to the equation

(P _(L) /P _(VE))_(maxn)=(P _(L) /P _(VE))_(max) −K _(n),

[0028] K_(n)=f((P_(Lkor)/P_(VE)); m_(Lkor)) being additionally filtered.

[0029] The gradient is calculated in the calculation unit 20.

[0030] In FIG. 1 the air pressure and air temperature sensor 14 is mounted upstream from the air filter 12 in the direction of flow. The air pressure and air temperature sensor 14 may also be provided in any other suitable place for measurement of ambient air pressure and/or ambient temperature. For example, the air pressure and the air temperature may be measured in a position situated downstream from the air filter 12.

[0031] In individual instances it may be advisable to equalize the boost pressure sensor with the ambient pressure sensor when the vehicle is not in movement, in order to reduce the tolerance.

LIST OF REFERENCE NUMBERS

[0032]1 Internal combustion engine

[0033]2 Intake pipe

[0034]3 Boost air cooler

[0035]4 Turbocharger

[0036]5 Compressor

[0037]6 Turbine

[0038]7 Air duct

[0039]8 Air duct

[0040]9 Air duct

[0041]10 Air mass gauge

[0042]11 Air duct

[0043]12 Air filter

[0044]13 Air duct

[0045]14 Sensor for air pressure and air temperature

[0046]15 Exhaust gas line

[0047]16 Exhaust gas line

[0048]17 Sensor for boost pressure and boost air temperature

[0049]18 Engine control device

[0050]19 Databank

[0051]20 Calculation unit 

1. A process for control of boost pressure limitation of a turbocharger in an internal combustion engine as a function of the density of ambient air, the values determined for the actual ambient temperature (T_(∞)), the actual ambient pressure (p_(∞)), for the air mass drawn in (m_(L)), and for the boost pressure (p_(L)) in this operating condition are determined at assigned time intervals and the actual pressure (p_(VE)) at the compressor intake and the actual temperature (T_(VE)) at the compressor intake being determined by way of predetermined air mass dependent correction curves, the air mass throughput (m_(Lkor)) at the compressor intake being adjusted to standard conditions from the pressure determined (p_(VE)) at the compressor intake, from the temperature (T_(VE)) determined at the compressor intake, and the determined air mass (m_(L)) drawn in, respectively, the maximum permissible compressor speed dependent boost pressure (p_(Lmaxkor)) being taken respectively from the compressor characteristic for the maximum turbocharger speed (n_(Vmax)) permissible air mass throughput (m_(Lkor)) adjusted to standard compressor conditions at the compressor inlet and the ambient pressure determined (p_(∞)) and being compared with the boost pressure (p_(List)) determined in this operating condition, and the boost pressure being controlled so that the value determined for the boost pressure (p_(List)) corresponds at the maximum in each instance to the maximum permissible compressor speed dependent boost pressure (p_(Lmaxkor)) determined in this state.
 2. The control process as defined in claim 1, the temperature (T_(VE)) being determined from the actual ambient temperature (T_(∞)) at the compressor intake and a predetermined air mass dependent correction parameter for the temperature (K_(T)) and the pressure (p_(VE)) at the compressor intake from the actual ambient pressure (p_(∞)) and a predetermined air mass dependent correction parameter for the boost pressure (K_(P)), and the adjusted air mass throughput (m_(Lkor)) at the compressor intake, pressure (p_(VE)), and air mass (m_(L)) drawn in, from the following relation: m _(Lkor) =m _(L)·((T _(VE)+273.15K)/Tov ^(0.5)(p _(VE) /P _(OV))), T_(OV) being the temperature at the compressor intake under standard compressor conditions and P_(OV) the pressure at the compressor intake under standard compressor conditions.
 3. The control process as defined in one or more of the preceding claims, the actual ambient temperature (T_(∞)) being measured for the actual ambient pressure (p_(∞))for the air mass (m_(L)) drawn in and for the boost pressure (p_(List)) and being transmitted to the engine control device, the compressor characteristic and the predetermined correction curves for determination of actual pressure (p_(VE)) at the compressor intake and the actual temperature (T_(VE)) being present in the engine control device and the actual pressure (p_(VE)) at the compressor intake and the actual temperature (T_(VE)), the adjusted air mass throughput (m_(LVE)) at the compressor intake, and the compressor speed dependent maximum permissible boost pressure (p_(Lmax)) being determined and the control signals for boost pressure control being generated in the engine control device.
 4. The control process as defined in one or more of the preceding claims, the boost pressure (p_(List)) being measured in the boost air duct between a boost air cooler and the combustion chamber of the internal combustion engine, an adjustment for pressure loss between compressor intake and boost pressure measurement point being made when the measured boost pressure (p_(List)) is compared with the respective compressor speed dependent maximum permissible boost pressure (p_(Lmax)) determined for this purpose, this adjustment/being accomplished in particular in that an adjusted maximum permissible boost pressure (p_(Lmaxkor)) with correction characteristic dependent on the air mass throughput (m_(LEV)) at the compressor intake is determined and then this adjusted maximum permissible boost pressure (p_(Lmaxkor)) is compared with the measured boost pressure (p_(L)), this adjusted maximum permissible boost pressure (P_(Lmaxkor)) being determined preferably by the correction factor (K_(PLLK)) dependent on the air mass throughput (m_(L)) measured at the compressor intake for the boost pressure loss, at least in the boost air cooler, in accordance with the equation p _(Lmaxkor) =p _(Lmax) ·K _(PLLK), with K _(PLLK) =f(m _(L)).
 5. The control process as defined in one or more of the preceding claims, on comparison of the measured boost pressure (p_(L)) with the respective compressor speed dependent maximum permissible boost pressure (p_(Lmax)) an adjustment being made for allowance for a dynamic component by means of the changes in engine speed over time, such adjustment being made in particular in that an adjusted maximum permissible pressure ratio ((P_(L)/P_(VE))_(maxn)) with a predetermined correction function (K_(n)) is determined in order to make allowance for the gradient of the engine speed (n) over time (t), and by preference this adjusted maximum permissible pressure ratio ((P_(L)/P_(VE))_(maxn)) being determined in accordance with the equation (P _(L) /P _(VE))_(maxn)=(P _(L) /P _(VE))_(max) −K _(n), with K _(n) =f((P _(Lkor) /P _(VE)); m _(Lkor)).
 6. The control process as defined in one or more of the preceding claims, in the case of a compressor intake path with built-in air filter the actual ambient temperature (T_(∞)) and the actual ambient pressure (p_(∞)) being measured upstream from the air filter in the direction of flow of the intake air.
 7. The control process as defined in one or more of claims 1 to 5, in the case of a compressor intake path with built-in air filter and with an air mass gauge the actual ambient pressure p_(∞) being measured downstream from the air filter in the direction of flow of the intake air and the actual ambient temperature (T_(∞)) being measured in the air mass gauge.
 8. The control process as defined in one or more of the preceding claims, adjustment of the sensor for measurement of the boost pressure (p_(List)) to the sensor for measurement of the actual ambient pressure (p_(∞)) being effected with the vehicle at rest.
 9. An internal combustion engine with exhaust gas turbocharger and with a control device for adjustment of the boost pressure for which respectively the actual boost pressure is determined and compared with assigned values for the assigned boost pressure in the respective operational state taken from a stored compressor characteristic and adjusted, characterized in that the control device is in data connection with means for determination of ambient temperature (T_(∞)), of ambient pressure (p_(∞)) from an air mass drawn in (m_(L)), and of boost pressure (p_(List)) and has means for recording such data at assigned intervals, in that the control device is in data connection with a databank which has stored in it predetermined air mass dependent correction parameters for the boost pressure (K_(P)) and the temperature (K_(T)) at the compressor intake of the turbocharger and with the stored compressor characteristic with respective predetermined relationships between air mass drawn in (m_(L)) and the ratio of boost pressure to ambient pressure (p_(L)/p_(∞)) for various compressor speeds (n_(v)) and for the maximum permissible compressor speed (n_(Vmax)) of the turbocharger, in that the control device has means for respective determination of the pressure (p_(VE)) at the compressor intake from the ambient pressure (p_(∞)) determined and the corresponding adjustment (K_(P)) of the pressure (p_(VE)) at the compressor intake and for respective determination of the temperature (T_(VE)) at the compressor intake from the ambient temperature (T_(∞)) determined and the corresponding correction parameter for the temperature (K_(T)), for respective determination of the actual value for the adjusted air mass throughput (m_(Lkor)) at the compressor intake from the air mass drawn in (m_(L)) as determined, from the pressure (p_(VE)) as determined and the compressor intake, and from the temperature (T_(VE)) as determined at the compressor intake, and for determination of the maximum permissible boost pressure (p_(Lmax)) for this adjusted maximum permissible air mass throughput (m_(Lkor)) from the compressor characteristic from the maximum permissible compressor speed (n_(vmax)) at the compressor intake for this adjusted air mass throughput (m_(Lkor)), and from the ambient pressure (p_(∞)) as determined and for respective comparison of the boost pressure (p_(List)) as determined and the respective compressor speed dependent maximum permissible boost pressure (p_(Lmax)) determined for this purpose, and in that the control means is connected to means for buildup and modification of the boost pressure and has a control mechanism for setting the upper limit of boost pressure buildup, which mechanism acts on the buildup means and acts to modify the boost pressure so that the boost pressure (p_(List)) does not exceed the maximum permissible boost pressure (p_(Lmaxkor)) as determined.
 10. The internal combustion engine as defined in claim 5, the control device and the databank being part of the engine control equipment.
 11. An engine control device for an internal combustion engine with exhaust gas turbocharger with a control unit for control of the boost pressure and a databank, characterized in that the control unit is in the form of means for acquisition of data regarding ambient temperature (T_(∞)), ambient pressure (p_(∞)), air mass (m_(L)) drawn in, and boost pressure (p_(L)) at assigned time intervals, in that the control unit is data connected for data acquisition to a databank in which are stored predetermined air mass dependent correction parameters for the boost pressure (K_(P)) and the temperature (K_(T)) at the compressor intake of the turbocharger and the stored compressor characteristic with the respective predetermined relation, for various compressor speeds (n_(v)) and for the maximum permissible compressor speed (n_(Vmax)) of the turbocharger, between air mass (m_(L)) drawn in and the ration of boost pressure to ambient pressure (p_(L)/p_(∞)), in that the control unit has means for respective determination of the pressure (p_(VE)) at the compressor intake from the data acquired for the ambient pressure (p_(∞)) and the corresponding correction parameter for the boost pressure (K_(P)) of the pressure (p_(VE)) at the compressor intake and for respective determination of the temperature (T_(VE)) at the compressor intake from the data acquired for the ambient temperature (T_(∞)) determined and the corresponding correction parameter for the temperature (K_(T)) for respective determination of the actual value for the adjusted air mass throughput (m_(Lkor)) at the compressor intake from the data acquired for the air mass (m_(L)) drawn in as determined, from the pressure (p_(VE)) as determined at the compressor intake and from the temperature (T_(VE)) determined at the compressor intake and for determination of the maximum permissible boost pressure (p_(Lmax)) for this adjusted air mass throughput (m_(Lkor)) at the compressor intake from the compressor characteristic from the maximum permissible compressor speed (n_(Vmax)) at the compressor intake from the compressor characteristic from maximum permissible compressor speed (n_(vmax)) at the compressor intake and from the ambient pressure (p_(∞)) as determined and for the respective comparison of the boost pressure (p_(List)) as determined and of the respective compressor speed dependent maximum permissible boost pressure (p_(Lmaxkor)), in that the control unit has a data connection for data transmission of control data to means for buildup and for modification of the boost pressure and has a control mechanism for setting an upper limit to boost pressure buildup, a mechanism which generates such control data as acts on the means for buildup and for modification of the boost pressure so that this computer speed dependent maximum permissible boost pressure (p_(Lmaxkor)) will not be exceeded. 